ADLIan

An additional comment. The U-value calculation from ProDave is wrong as there is no correction for the timber frame creating a thermal bridge (normally 15% bridged proportion) and this would increase the U-value to nearer 0.16 W/m2K.

Most of the insulation manufacturers in the UK will provide a U-value and condensation analysis calculation. Some may also do the thermal response/phase shift numbers. Note that it is NOT accepted good practice to render onto insulation onto the timber frame - see 'Timber Frame Construction' from TRADA, Bldg Reg Approved Docs, TF kit manufacturers details etc. One of the wood fibre insulation manufacturers had a BBA certificate for a direct render system but this appears to have lapsed or been withdrawn. The issue is not so much condensation but liquid water penetration through the render system as referenced by Mr Punter.

They’re only the soakers ar each course of slate. Lead cover flashing (longer length, approx 1~1.5m) still needs fixing, chased into wall.

Is this new build house or extension? For new build expect U=0.15 or better. For extensions BR require 0.18 or better +1 to most of the above, especially multi foil! I would not bother with Frametherm 32 (extra cost for minimal improvement on U-val especially timbers at 400mm c/c) - go for 35 version. Fully fill the rafter space with this, breather membrane, counterbatten, batten & slate with 50mm PUR under rafter. Note this is not a warm roof. It gives a warm roof space but to be a warm roof construction the majority of the insulation must be above the rafters.

U-vals are always for the whole wall (or other element). Old cfc blown pur had lambda of approx 0.020 W/ mK but expect this to degrade considerably in this application to nearer 0.03 W/mK.

Expect U=0.43 at best, perhaps 0.45.

Normal quilt loft insulation cut to fit between timber. Leave last few feet rolled up and push/unroll into place with help of a broom. Add further layers same way if needed.

I was involved in that testing program. No real surprises from this testing compared to standard BBA recommendations, especially hit and miss issues with blown products.

Check product BBA cert. Subject to certain caveats full fill, especially at 300mm, can often be used in any exposure zone. 50mm clear cavity safer still.

Plenty of pur/pir alternatives but kingspan has a virtual monopoly on phenolic foam so expect to pay top dollar for it.

Modern mineral wool cavity batts are quite dense and rigid so the normal plastic retaining collars that slip over the wall ties will work OK. Why not just fully fill with 300mm (2x150mm) with no residual cavity? Where is the building located? Partial fill normally only needed in very exposed locations (SW England, west Wales & west Scotland) or high rise (18m or more in height) but rainwater penetration is very unlikely across 300mm full fill.

The thermal conductivity will be whatever the manufacturer states and is backed up by CE marking, the DoP and perhaps BBA certification. (Note post Grenfell Celotex were guilty of over stating both thermal and fire performance of certain products and I believe had BBA certificates suspended). The compressive strength may vary depending on application and if load bearing or not. You would need to check with the manufacturer for exact values of certain physical properties but they may not be forthcoming with very detailed (commercially sensitive?) information.

On a very simple level product used in flat roofing has to cope with temps varying from say -10 C to perhaps 80+C and the foam/facings have to be formulated to cope with this. Flooring, cavity wall and 'general purpose' PIR products will never be subject to this temp variation. (Individual manufacturers may be able to offer more detailed info on the make up their products). Bottom line is the products are optimised for the application they are made for - hence swapping products/applications or using second grade product may lead to problems.

PUR and PIR may have slightly different chemical compositions depending upon application. Flat roof products for example face much more difficult conditions 'in use' compared to say a flooring application. The facings may also be different. What you see as a 'foil' face may have many different layers from a simple single layer to 11 layers or more depending upon application. Specific products based on the above variations may also be BBA approved for a particular application. An alternative view is it's all marketing and sales hype and the products are actually the same!

@ProDave SAP energy rating is based on energy costs and these are normally increased (inflation?) in new versions of SAP so your SAP/EPC will probably remain the same. The big difference is reducing the carbon intensity of electricity (fewer coal fired power stations) so should make Building Reg compliance of all electric houses easier.

For Building Reg compliance no. You have to comply with Regs and associated SAP version in force at time of application.

@Visti Not sure what stage you are at with Building Regs but SAP10 will not be used in foreseeable future. Most likely will be introduced in next update of Part L - sometime in 2020?

Check with the PUR manufacturers. Generally foil faced boards are mechanically fixed whilst those for bonding have a coated glass tissue facing (normally cream/off white in colour). Remember you will also need a VCL on the deck prior to the the insulation boards and you cannot bond to polythene so fully bonded PUR normally goes onto a fully bonded bituminous felt VCL.

The grant aided schemes are normally for upgrading existing lofts and are often means tested. Loft conversions come under the Building Regs along with the requirement for insulation at the roof line or flat roof. I assume the thinking is if you can afford a loft conversion then you can afford the insulation to go with it.

I see this a lot as a planning condition. Typically Planners will require a 'scheme' to be 10% better than Regs based on CO2 emissions and/or fabric energy efficiency and also may dictate it's got to be done by the use of renewables. Distinct lack of consistency even within one planning authority! Self builders and smaller developers have to jump through the hoops but, as ever, the large, national house builders appear to avoid this type of condition, I believe the reason(?) is 'it doesn't make the development economically viable'. Ian

Rockwool data I have shows cavity batts below DPC starting just above the lean mix cavity fill - I believe this is common to just about all manufacturers and BBA certs

Beg to differ. You will find just about all built in cavity insulation products are BBA certified for use below DPC

A ground floor U-value of 0.3 W/m2K would give an automatic fail under the English Regs - must be 0.25 W/m2K or less, area weighted average. 100mm PUR probably gives better than U=0.2 in a typical floor, perhaps closer to U=0.16. This can easily be offset elsewhere in the construction. Note the DER/TER requirement can still be easily met depending upon fuel, heating system - air source heat pump, addition of solar PV etc helping reduce CO2 emissions. High individual U-values will impact on the DFEE/TFEE however and will be more difficult to resolve.

The nail plate is shown with a conductivity of 17 W/mK - this is the value for stainless steel. For typical nail plate, in galv steel, this should should be 50-60 W/mK. But, as above, probably has little impact on U-value, probably only in 3rd decimal place and probably less than 0.01 W/m2K. Not sure its worth worrying to much about these slight variances in U-values when effect of linear thermal bridges may be your biggest enemy!

Should also take the opportunity to add/upgrade the insulation. Probably falls under Appr Doc L1B requiring this upgrade.